Ionization in Unstriated Discharge and in the Arc. 277 



single reed. The double reed, as used on the oboe and 

 bassoon, consists of two blades which are hollowed out so 

 that when the blades are secured together there is an elliptical 

 space between the blades. Now, in order definitely to alter 

 the length of blade which is free to vibrate, the lips would 

 have to squeeze the reed so hard that the blades would be 

 pressed together. Such an action is of course impossible, 

 since the passage of air through the. reed would be stopped. 

 The vibrating length, therefore, can be damped more or less 

 where the' lips are pressed on the reed but cannot be defi- 

 nitely altered. Hence it is, I think, that mere alteration of 

 lip pressure is insufficient to produce the higher notes on 

 wind instruments employing double reeds. In the case of 

 single reeds, however, the lower end of the free portion of 

 the reed adjacent the lower end of the bevel or " lay," as it is 

 called, of the mouthpiece, may be pressed firmly against the 

 mouthpiece so as definitely to shorten the vibrating length 

 of the reed, and yet an air-passage will still be left between 

 the reed and mouthpiece. 



XXXI. Ionization in the Unstriated Discharge and in 

 the Arc. By C, 1). Child *. 



SO far as the writer of this article is aware, no satisfactory 

 explanation has been given for the relation existing 

 between the current in the unstriated discharge and the rate 

 at which the ions recombine, nor for the relation between 

 the electric force and the pressure of the gas. The following- 

 explanation is therefore suggested. This discussion applies 

 also to those forms of the arc which have the same cross- 

 section at all parts, as does the mercury arc. 



Recombination of the Positive and Negative Ions. 



A discussion of this topic was given by H. A. Wilson f a 

 few years ago, but his fundamental equations lead to con- 

 clusions which appear at the present time to be incorrect, as 

 is shown by the following. These equations are the ones 

 commonly used in cases where a current is carried by ions 

 formed in a gas, namely, 



i = en(u-\-v) and N = om 2 , 



where i is the current per unit cross-section, e is the charge 

 carried by each ion, n the number of positive and also of 



* Communicated by the Author. 

 t Phil. Mag. [6] vi, p. 160 (^lUOS). 



